There is probably a piece of wood trim above the top of the TV that keeps it from moving up. If you remove the 3 screws holding the trim, and slip the trim out of the way, you can lift the TV off of it's mount and you can probably balance it on the counter. Probably a good idea to have a 2nd person there to help.
You may have to route the cable through holes in the woodwork. A coat hanger and a flashlight will help you find and grab the cable. Again, a 2nd person is needed to hold the TV while you do the routing.
As long as you're routing cables, you might want to take a look at
this guide in the manuals section of the Forum and add additional cables to connect the TV audio to the Surround Sound System.
When putting it back on the mount, there are probably TWO brackets on the wall; one high, one low. The corresponding brackets on the TV have to engage with both to hold the TV securely. After you're sure you have it back in place, put the trim back.